Which preposition to use with floodgates

of Occurrences 14%

But that day it rained as if the floodgates of heaven had opened.

on Occurrences 1%

Her instantaneous resumption of the serving-maid's relation to him jarred on Willan at that second indescribably, and shut down like a floodgate on the words he was about to speak.

Which preposition to use with  floodgates